The invention relates to a device for the storage of digital information in the form of magnetic bubbles in a magnetizable layer located in a bias magnetic field which extends transverse to the layer. The device comprises a number of drive patterns which are in the form of contiguous disc patterns of mainly a first scale. Each of the drive patterns comprise a generator element for generating magnetic bubbles which represents a first access element, and a detector element for detecting magnetic bubbles which represents a second access element. Each of the access elements comprise an excitation loop which can be selectively controlled by an electric current. A rotary field generator is provided for driving bubbles along the relevant drive patterns by way of a rotary magnetic field.
A device of this kind is known from the article by G. Almasi, et al entitled "Nucleation of 1-.mu.m" "Bubbles via Charged Walls" (IEEE Trans. on Magnetics, Vol. MAG-16, No. 1, Jan. 1980, pages 89-93. A contiguous disc pattern is to be understood to mean herein a pattern of contiguous more or less disc-shaped elements or rhombic elements. It is formed, notably, by local implantation of ions. Small scale deviations from the basic shape may occur due to edge effects. Due to the fact that the disc patterns are contiguous, the drive patterns have the appearance of straight or curved strips whose edges exhibit a given serration. The domains are driven along these edges. The scale can be defined, for example, as the mean period of the serration.
FIG. 4 of the article by Almasi et al shows a number of drive patterns, each of which comprises a generator loop. The generator loops being electrically connected in series.
The advantage of this contiguous disc technology is that the sizes of the magnetic bubbles may be comparatively small with respect to the smallest detail of the geometry of the drive patterns (for example, in comparison with drive structures comprising T-shaped and I-shaped patterns of vapor-deposited permalloy). If the smallest details to be realized have a fixed dimension which is determined by the technology, therefore, comparatively small bubble diameters can be used. As a result, a high information density can be realized. Due to the small diameters of the bubbles used, the scale of the excitation loops will be large in comparison with the dimensions of the magnetic bubbles. Thus, the mutual positioning of drive patterns and excitation loops is subject to severe requirements as regards accuracy.